1. Field of the Invention
The present invention relates to a laminate and also relates to a display filter, and particularly, to a transparent conductive laminate having high quality and durability and to a display filter.
2. Description of the Related Art
With the progress of a multimedia society and a digital society, image information and digital information transmitted, allotted or processed are increasing outstandingly. The importance of display devices that are monitors displaying the information is more increased as interfaces or key devices connecting human beings with communication devices, imaging devices and computers.
As such a display device, various thin type displays are studied energetically in place of conventional cathode ray tube (CRT) monitors which are heavy and thick and have a difficulty in developing a large-sized display device. Much attention is focused on plasma display panels (PDP), field emission displays (FED) and the like among these thin type displays which make it relatively easy to realize thin type and large-sized displays.
Particularly, PDPs have reached a mass-production stage and each maker comes out with a plan for increasing the output of PDPs so as to double the output every year. On the other hand, there are makers announcing that they are newly entering the field of PDPs and it is therefore expected in newspapers and the like that the market of these PDPs will be rapidly expanded.
These PDPs have the advantages in developing thin and large-scaled products. However, they have the problem that because they utilize a discharge phenomenon, they generate an intensive electromagnetic wave leakage in principle. For this, it becomes necessary to suppress the electromagnetic wave leakage generated from a plasma display within a safe standard value (for example, VCCI (Voluntary Control Council for Interference by data processing equipment electronic office machine) in Japan and FCC (Federal Communication Commission) in USA.
Also, the PDP emits intense near-infrared rays. Because wireless LANs, cordless phones, infrared remote controllers and the like are devices utilizing near-infrared rays, it is pointed out that there are the possibilities of the PDP causing the malfunction of these devices. From the above fact, the PDP must be provided with a means for decreasing a electromagnetic wave leakage to the above defined range to shield light in a wavelength range from 800 to 1000 nm which is the near-infrared range to a level where the malfunction is not substantially caused.
The electromagnetic wave and near-infrared rays as mentioned above can be restrained from being emitted by coating the whole PDP with a conductive material such as a metal. However, it is necessary to use a material having not only conductivity but also transparency on an image display part. For this, a filter having transparency and conductivity is preferably used on the display part of the PDP. Preferable examples of such a display filter include transparent conductive thin-film type optical filters prepared by arranging a transparent conductive thin-film on the entire surface of a substrate such as a glass substrate. As the transparent conductive thin-film type optical filter, those having a laminate structure constituted of a transparent conductive thin-film that cuts electromagnetic waves and a film having an anti-reflecting function and a glare-proof function are known.
It is needless to say that the electromagnetic wave-shielding ability of a display filter is higher with a decrease in the surface resistance thereof. Therefore, silver that has the lowest specific resistance among pure materials or a metal thin film constituted primarily of silver is preferably used as the foregoing transparent conductive thin film. Actually, it is usual to make a laminate, prepared by sandwiching a metal thin-film layer mainly containing silver between transparent high-refractive index thin-film layers, as the transparent conductive thin film for the purpose of raising transmittance and improving the stability of the metal thin-film layer.
However, as is well known, there is a large problem that silver which is preferably used as the metal thin-film layer material generates an aggregate of atoms very easily. When silver atoms of the silver thin-film layer aggregate, not only are the low-resistance characteristics required for a metal thin film impaired but also silver white spots (also called spot defects, reflection defects or white spots) are produced. When many reflection defects are produced in a display filter, these reflection defects appear as white spots on a number of forceful images projected on a plasma display to which the filter is set, producing the harmful effect of deteriorating image quality. As mentioned above, the reflection defects give rise to a large problem that the characteristics such as high transparency and low-resistance characteristics which the metal thin-film material has are lost and these defects also deteriorate product quality as a filter.
It is conventionally known that the aggregation of silver atoms in the silver thin-film layer occurs easily in the presence of a chlorine ion and foreign substances (particles). Along with the development of a large-sized screen which is desired in the market, the number of particles intermingled per filter is expected to be increased. In this situation, the number of white spots generated in each filter increases and it is expected that the yield of the filter is decreased. Therefore, in optical filters for PDPs which are more increased in size, techniques for preventing the occurrence of white spots on the silver thin-film layer more efficiently are considered to be more desired in the future.
Attempts to remove foreign substances and chlorine like the above are reported in each publication of JP-B No. 59-44993 and JP-A No. 9-331488. However, in order to produce a filter for large-sized displays at a high yield, it is required to suppress the aggregation of silver atoms at a high level.
On the other hand, attempts have been made to prevent the chlorine ion and the like from reaching the silver thin-film layer by making thick the transparent high-refractive index thin-film layer. However, it is demanded of an optical filter to have high transparency as mentioned above. There is therefore a limitation to the thickness of the transparent high-refractive index thin-film layer and there is a limitation in applying the above method.
As other attempts, there is a method in which a metal thin film such as copper or platinum which has corrosion resistance is laminated on the silver thin-film layer. However, this method has the problem that it is accompanied by a reduction in transparency and a rise in surface resistance.
To mention the present state of art, no display filter having a structure which can easily prevent the occurrence of reflection defects has been obtained so far as mentioned above.
In the meantime, radio devices and electronic devices have been recently developed outstandingly and a demand for these devices has been increased. Radio devices are convenient but, on the contrary, has such a danger that electromagnetic waves in use are monitored by others and the information which these electromagnetic waves have is read. Not only in these radio devices but also in electronic device, electromagnetic waves are generated from cords beside the body and monitored by others and the information of these electromagnetic waves is read easily in the same manner as in the case of radio devices. There has been an increased demand for electromagnetic wave-shielding materials in recent years to suppress the leakage of information associated with the leakage of electromagnetic waves. Although electromagnetic waves can be cut by conductive materials such as a metal, there is a demand for materials, such as those used for windows of various buildings, car windows and display parts of various display devices, for which transparency in addition to electromagnetic wave-shielding ability is required. Also, it is demanded of materials used in applications such as windows to have heat-ray reflecting ability for the purpose of saving energy by increasing cooling efficiency in buildings in a summer season.
In order to attain these electromagnetic wave-shielding ability and heat-ray reflecting ability, the above thin film containing silver as its major component has preferable natures. However, in these applications like the case of the above display, there are problems such as a decline in product quality caused by the generation of white spots, a reduction in yield and a reduction in life and it is therefore desired to suppress the aggregation of silver atoms at a high level.